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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Aegopogon Humb. & Bonpl. ex Willd.

From the Greek aix (goat) and pogon (beard), referring to fascicles of awns.

~ Muhlenbergia sensu lato

Including Atherophora Steud., Hymenothecium Lag., Schellingia Steud.

Habit, vegetative morphology. Delicate annual. Culms 6–30 cm high; herbaceous. Leaves not basally aggregated; non-auriculate. Sheaths loose. Leaf blades linear; narrow; 1–2 mm wide; flat; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite, male-only, and sterile. The male and female-fertile spikelets mixed in the inflorescence (in triads, the central member hermaphrodite, the laterals male or sterile). The spikelets overtly heteromorphic.

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (the main axis bearing triplets of spikelets with short flat pedicels, the triplets short-pedunculate, spreading, the rachis filiform); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating; falling entire (i.e. the triplets falling). Spikelets in triplets; secund (the triplets on one side of the axis); sessile and pedicellate, or subsessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations, or unequally pedicellate in each combination (the central hermaphrodite spikelet sessile or subsessile, the reduced laterals pedicellate). The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only, or sterile.

Female-sterile spikelets. The longer-pedicelled male or neuter spikelets reduced.

Female-fertile spikelets. Spikelets 2 mm long; compressed laterally, or not noticeably compressed, or compressed dorsiventrally (?); falling with the glumes (the triplets disarticulating, with the pointed basal stipe). Rachilla terminated by a female-fertile floret.

Glumes present; two; more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; free; not pointed (apically notched); awned (via the extended midnerve); similar (membranous, truncate or notched, awned). Lower glume 1 nerved (?). Upper glume 1 nerved (?). Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas similar in texture to the glumes (membranous); not becoming indurated; incised; with a narrow, nerveless lobe outside each lateral awn; not deeply cleft; awned. Awns 3; median and lateral; the median similar in form to the laterals; continued from the nerve; non-geniculate (delicate); hairless (scabrous); much longer than the body of the lemma; entered by one vein. The lateral awns shorter than the median. Lemmas hairless; without a germination flap; 3 nerved. Palea present; relatively long (but somewhat shorter than the lemma); apically notched; awned (two-awned); textured like the lemma; not indurated; 2-nerved. Lodicules present; 2; fleshy; glabrous. Stamens 3. Anthers small. Ovary apically glabrous. Stigmas 2.

Fruit, embryo and seedling. Fruit small (about 1.7 mm long in A. bryophylus); fusiform, or ellipsoid; compressed laterally. Hilum short. Pericarp fused. Embryo large; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae not over-arching the stomata (for the most part); consisting of one oblique swelling per cell (large). Mid-intercostal long-cells rectangular; having straight or only gently undulating walls. Microhairs present; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhair basal cells 30 microns long. Stomata common. Subsidiaries non-papillate; dome-shaped (sometimes approaching parallel). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (solitary); not silicified. Intercostal silica bodies absent to imperfectly developed. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; confined to the central file(s) of the costal zones to present in alternate cell files of the costal zones; ‘panicoid-type’; cross shaped to dumb-bell shaped.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheaths of the primary vascular bundles complete. PCR sheath extensions absent. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (the large median cell of each group deeply inserted in the mesophyll). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the main bundles); forming ‘figures’ (the main bundles with anchors). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Muhlenbergiinae (as a synonym of Muhlenbergia). 3 species.

Distribution, phytogeography, ecology. Southern U.S.A. to Argentina.

Rusts and smuts. Rusts — Puccinia. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.

References, etc. Leaf anatomical: this project.

Illustrations. • A. cenchroides: P. Beauv. (1812). • A. tenellus (Hitchcock and Chase, 1950)


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Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 13th November 2017. delta-intkey.com/grass’.

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